Techniques for casting encapsulated coils

ABSTRACT

Disclosed is a vaporization cooled inductive apparatus. The apparatus comprises a winding assembly encapsulated in a cast body of solid insulating material and disposed in a sealed tank. The cast winding assembly includes at least one liquid absorbent wick and a vaporizable liquid containing reservoir. The wicks carry said liquid to hot interior regions of the winding. Condenser means are provided for recycling vapors produced during the cooling process.

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ycling vapors 8 Claims, {Drawing Figures United States Patent Nicholss41 TECHNIQUES FOR CASTING ENCAPSULATED COILS [72] Inventor: Thomas G.Nichols, Rome, Ga.

General Electric Company May 10, 1971 [73] Assignee:

[22] Filed:

[2]] Appl. No.:

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1 TECHNIQUES FOR CASTING ENCAPSULATED COILS BACKGROUND AND OBJECTS OFTHE INVENTION monly utilized in such lower power electrical apparatus asmotor starters and other control devices. Whi1e resin encapsulationdiminishes the ability of an electric coil to dissipate heat generatedby the current passing through it, heat generation has generally notproven to be a critical or limiting parameter in low power electricaldevices having current ratings at the level of control or communicationcircuits. I

In design of electrical induction apparatus for high power applications,such as transmission and supply transformers and reactors for utilityand industrial applications, it has long been recognized that dielectricstrength close to the winding could be improved by encapsulating themain high power windings in solid insulating material, and that overallsize and weight of the apparatus could be reduced accordingly. However,solid encapsulation of large multi-layer windings of high power ratingintroduces severe cooling problems not usually susceptibletosatisfactory resolution by the otherwise common expedient of immersingtransformer coils in oil or other liquid cooling media. Casting resinshaving good electrical insulating qualities are generally not good heatconductors, so that a resin-sheathed coil tends to retain internallygenerated heat.

Accordingly, it is a general object of my invention to provide new andimproved cooling means for electrical induction apparatus having coilwindings sheathed in solid thermosettin'g insulating material.

It is a more particular object of my invention to provide improved meansfor utilizing a vaporizable liquid to cool resinencapsulated coilassemblies in high power electric induction apparatus.-

SUMMARY OF THE INVENTION In carrying out my invention in a preferredform I encapsulate the main winding assembly of an electric powertransformer in a cast body of epoxy resin by disposing a first layer ofsaid resin about and in intimate contact with a winding layer. Liquidabsorbent means is disposed similarly about said resin layer foreffectuating vaporization cooling of said winding assembly. A secondlayer of epoxy resin is disposed about the liquid absorbent means and areservoir containing a vaporixable liquid coolant is provided adjacentthereto with a portion of the absorbent means being immersed in theliquid. The liquid absorbent means is adapted for transporting theliquid coolant from the reservoir to the surface of the epoxy layer inintimate contact with the winding layer so that thewinding-generated-heat may be extracted by said liquid as it vaporizes.Condenser means are provided to convert the resulting vapor into liquidform and return it to the winding assembly.

The winding assembly may include a plurality of concentric windings eachwinding of which may be encapsulated and cooled in the above describedmanner.

In accordance with one embodiment of my invention the liquid absorbentmeans comprises a wick material which is disposed about and in intimatecontact with said first resin layer.

In accordance with another embodiment of my invention the liquidabsorbent means comprises a pair of wicks which are separated from oneanother by a passageway. This variant arrangement enables unrestrictedvaporization of the cooling liquid from a lateral surface of each annualwick. Unrestrained vaporization serves to effectuate efiicient heatextraction. The passageway also serves to enable the cooling processproduced vapors to freely flow to the condenser and in so doing itenables the reliquifrcation of those vapors to occur within a relativelyshort time after vaporization.

In either embodiment the wick arrangement serves to effectuate efficientcooling of the winding by insuring that maximum wetting of the epoxylayer in intimate contact therewith occurs.

DESCRIPTION OF THE DRAWINGS I My invention will be more fully understoodand its various objects and advantages further appreciated by referringnow to the following detailed specification taken in conjunction withthe accompanying drawings in which:

FIG. I is a vertical cross sectional view, partially in section, of avaporization cooled transformer in accordance with my invention.

FIG. 2 is a cross sectional view of a portion of the winding DETAILEDDESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, there isillustrated generally an induction apparatus or transformer 1 inaccordance with my invention. The transformer comprises a magnetizablecore 2 and an associated winding assembly 3 disposed within a sealedenclosure or tank 4. The winding assembly 3 comprises a high voltagewinding and a low voltage winding each of which is concentricallydisposed about a leg of core 2. Each winding includes a plurality ofwinding layers and each layer may be constmcted of single or multistrandelectrical conductor. I

As can be seen in FIG. 2, winding 3 comprises an annular low voltagewinding 5 and an annular high voltage winding 6. The low voltage windingis made up of four winding layers, namely, 5a, 5b, 5c and 5d. The highvoltage winding 6 is made up of nine winding layers, namely, 6a, 6b, 6c,6d, 6e, 6f, 6 6h and 6i. Electrical insulation between high and lowvoltage windings is provided by disposing a solid insulating sleeve 7between such windings.

The assembly 3 is cast into a compact integral unit by disposing glassmesh roving material 8 about selected winding layers, impregnating theroving with a thermo-setting resin or epoxy 9 and encapsulating theentire assembly in the same cast resin.

In order expeditiously to extract heat generated by the windings duringtheir operation I have included novel cooling means in the windingassembly 3. My cooling means operate on the principle of vaporizationcooling. As is known in the art, vaporization cooling is a techniqueutilizing the phenomenon that a fluid, in changing from a liquid to agas, absorbs a large amount of heat (i.e., an amount of heat equal toits heat of vaporization) from any hot body in contact with it without atemperature increase above the boiling point of the liquid.

As can be seen in FIG. 2 the integrally cast winding assembly 3 includesa bottom reservoir 14 containing a vaporizable liquid coolant. Liquidabsorbing means are provided to carry the liquid from the reservoir andalong the peripheral surface of the several epoxy coated winding layerswherebythe liquid vaporizes and in so doing extracts heat generated inthe winding interior.

In accordance with one embodiment of my'invention the liquid absorbingmeans consists of annular wicks 12a, 12b and 12a. As can be seen in FIG.2 two wicks, 12b and 12c, are provided in the high voltage winding andone wick, 12a, is provided in the low voltage winding. The number ofwicks utilized in any particular winding is dependent upon the amount ofheat generated therein. The number of wicks shown in FIG. 2 is thereforepurely exemplary.

Each wick is composed of a liquid absorbent material, for example duckcloth, and is arranged so that its lower extremity is immersed in theliquid contained in reservoir 10. When arranged in this manner the wickscarry the liquid coolant, via capillary action, from reservoir to theabutting epoxy layers adjacent the windings, whereby complete wetting ofthe epoxy layers occurs without the formation of coolingefficiencyrobbing rivulets.

As can be seen in FIG. 3 an insulating polyester film of sheet material13 is provided on each side of the wick means so that during fabricationof the winding assembly, liquid epoxy will be prevented fromimpregnating the adjacent wick. However, it is desirable that the castepoxy adhere closely to the polyester film, so that heat transfer fromthe winding layers through the epoxy layer and the film to the'liquid inthe wick will not be appreciably impeded.

In operation, the heat generated by the electric current flowing throughthe winding layersis conducted through the epoxy layers encapsulatingthose winding layers. The vaporizable liquid is carried by the wicksfrom the reservoir to said epoxy layers, whereby some of the heat isabsorbed by the liquid and its temperature is increased thereby. Whenthe boiling point of the liquid is reached, a large amount of heat,equal to the heat of vaporization of the liquid, is absorbed without afurther increase in temperature of the liquid. The vapors which resultfrom the vaporization of the liquid travel upward through-the wick andeventually leave the wick at its upper edge or edge region.

A filler material 14, such as a closed cell foam, is provided insideenclosure 4, as shown in FIG. 1. The filler occupies a large volume-inthe enclosure and thus forces the vapors to collect in the upper'portionthereof. This collected vapor is recycled into liquid form for reuse inthe vaporization cooling process. To that end, and by way ofillustration, I have shown in FIG. ,1 a condenser 16 built into the lidof tank 4 and containing a plurality of cooling tubes 17a and 17b. Thecooling tubes are adapted for converting thecooling-processproduced-vapors into liquid droplets and for returningthem to the winding assembly. For example, the liquid dropletscondensing on tubes 17a fall into a liquid trap 18. The liquid collectedin this trap is conducted via tube 18a back into the reservoir 10. Theliquid droplets condensing on tubes 17b fall onto the upper portion ofthe winding assembly where they wet the upper extremities of the wicks.This arrangement expedites the vaporization cooling process byeffectuating a fuller wetting of the wicks.

FIG. 4 is a perspective view of a portion of the high voltage winding 6with a modified liquid absorbing means. In this embodiment of myinvention, in lieu of the wicks shown in FIG. 2, I utilize absorbentmeans including a pair of liquid absorbent wicks 19 interposed betweenadjacent winding layers. The wicks 19 are separated from one another byinsulating spacers 20 to provide a vapor passageway or space 21therebetween. The purpose of this space is to enable the liquid in thewicks to vaporize from a lateral surface of each wick withoutappreciable restraint. Since unrestrained vaporization effectuatesmaximum heat absorption efficiency, this modification is particularlyuseful in high power winding assemblies. Furthermore, the space betweenthe wicks serves as an unobstructed passageway through which the vaporstravel to the condenser. This enables the recycling of the vapors backinto the liquid form soon after their vaporization in the wicks.

As should be appreciated a polyester film is not provided on each sideof the wicks in this embodiment since this would impede the egress ofthe vapors from the wicks 19 into the passageway 21. Rather, a polyesterfilm is provided on each wick between it and the abutting epoxy layer(although such a construction cannot be seen in FIG. 4).

While I have shown and described a particular embodiment of myinvention, it will be obvious to those skilled in the art that variouschanges and modifications may be made without departing from myinvention in its broader aspects; and I,

therefore, intend herein to cover all such changes and modifications asfall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is: I

1. An electrically inductive apparatus comprising:

a. a sealed tank;

b. a winding assembly disposed within said tank, said assemblycomprising:

i. an electrically conductive winding layer, said wining layergenerating heat upon the passage of electric current therethrough;

ii. a first insulating means comprising a thermosetting resin disposedabout and in contact with said winding layer;

iii. a first liquid absorbent wick disposed about and in contact withsaid first insulating means;

iv. a second insulating means comprising a thermosetting resin disposedabout said wick;

v. a liquid reservoir disposed adjacent to said winding layer and saidwick;

vi. a vaporizable liquid disposed in said reservoir and in contact witha portion of said wick, said first wick being adapted for carrying theliquid to said first insulating means whereupon the heat generated bysaid winding layer is absorbed by said liquid as said liquid vaporizes;and

c. condenser means for converting the resulting vapors into liquid formand for returning a portion of said liquid to said reservoir.

2. The .inductive apparatus as specified in claim 1 wherein aninsulating film is disposed on said first wick and in contact with saidfirst insulating means.

3. The inductive apparatus as specified in claim 1 wherein saidcondenser means is disposed in said tank above said winding assembly andwherein a filler material is provided within said tank and disposedabout said winding assembly.

4. The inductive apparatus as specified in claim 1 wherein said firstwick has an upper and a lower extremity and wherein said reservoir isdisposed adjacent to the lower extremity of said wick and wherein saidcondenser means also returns a portion of said liquid to the upperextremity of said wick.

5. The inductive apparatus as specified in claim 1 wherein a secondliquid absorbent wick is disposed about said first wick between saidfirst wick and said second insulating means, said first and second wicksbeing spaced apart from one another to define a vapor passagewaytherebetween.

6. The inductive apparatus as specified in claim 1 wherein a vaporpassageway is provided between said first wick and said secondinsulating means. 7

7. The inductive apparatus as specified in claim 5 wherein said firstwick has an upper and a lower extremity and wherein 7 said reservoir isdisposed adjacent to the lower extremity of said wick and wherein saidcondenser means also supplies a portion of said liquid to the upperextremity of said wick.

8. The inductive apparatus as specified in claim 7 wherein a fillermaterial is provided within said tank and disposed about said windingassembly.

1. An electrically inductive apparatus comprising: a. a sealed tank; b.a winding assembly disposed within said tank, said assembly comprising:i. an electrically conductive winding layer, said wining layergenerating heat upon the passage of electric current therethrough; ii. afirst insulating means comprising a thermosetting resin disposed aboutand in contact with said winding layer; iii. a first liquid absorbentwick disposed about and in contact with said first insulating means; iv.a second insulating means comprising a thermosetting resin disposedabout said wick; v. a liquid reservoir disposed adjacent to said windinglayer and said wick; vi. a vaporizable liquid disposed in said reservoirand in contact with a portion of said wick, said first wick beingadapted for carrying the liquid to said first insulating means whereuponthe heat generated by said winding layer is absorbed by said liquid assaid liquid vaporizes; and c. condenser means for converting theresulting vapors into liquid form and for returning a portion of saidliquid to said reservoir.
 2. The inductive apparatus as specified inclaim 1 wherein an insulating film is disposed on said first wick and incontact with said first insulating means.
 3. The inductive apparatus asspecified in claim 1 wherein said condenser means is disposed in saidtank above said winding assembly and wherein a filler material isprovided within said tank and disposed about said winding assembly. 4.The inductive apparatus as specified in claim 1 wherein said first wickhas an upper and a lower extremity and wherein said reservoir isdisposed adjacent to the lower extremity of said wick and wherein saidcondenser means also returns a portion of said liquid to the upperextremity of said wick.
 5. The inductive apparatus as specified in claim1 wherein a second liquid absorbent wick is disposed about said firstwick between said first wick and said second insulating means, saidfirst and second wicks being spaced apart from one another to define avapor passageway therebetween.
 6. The inductive apparatus as specifiedin claim 1 wherein a vapor passageway is provided between said firstwick and said second insulating means.
 7. The inductive apparatus asspecified in claim 5 wherein said first wick has an upper and a lowerextremity and wherein said reservoir is disposed adjacent to the lowerextremity of said wick and wherein said condenser means also supplies aportion of said liquid to the upper extremity of said wick.
 8. Theinductive apparatus as specified in claim 7 wherein a filler material isprovided within said tank and disposed about said winding assembly.